What is “the most contentious issue of our times”? According to Penn State professor Michael Mann, it’s climate change.

Mann, the author of The Hockey Stick and the Climate Wars: Dispatches from the Front Lines, sat down with Michael Smerconish on POTUS Politics to talk about his research, which has entered the spotlight now that President Barack Obama has announced an ambitious plan to combat climate change.

Obama’s plan includes three components: cutting carbon pollution in America, preparing the United States for the effects of climate change and leading international efforts to address global climate change.

“As a president, as a father and as an American, I’m here to say we need to act,” Obama said to an audience of environmentalists, politicians and students in a speech at Georgetown University last week.

The president’s proposal has received criticism from some, including Rep. Bill Johnson (R-Ohio), who discussed the plan on The Morning Briefing with Tim Farley.

“We could have solved [climate change] years ago if we had invested in clean coal technology rather than buying energy from sources overseas that don’t like us very much,” Johnson said. “This is an attack on the coal industry, this is an an attack on the jobs that are created by the coal industry and it’s an attack on middle-class Americans here in Eastern and Southeastern Ohio that depend upon cost-affordable, reliable energy.”

The president’s plan would end public financing for new coal plants overseas and require the Environmental Protection Agency to complete new pollution standards for power plants.

Others have supported the president’s climate push and taken note of its importance to his second term. “This is a sign that Obama really does want to make this a legacy of his time in the White House,” Amy Hardner, an energy reporter for the National Journal, said on POTUS Politics.

Though Obama’s plan bypasses Congress, the president stressed the importance of bipartisan cooperation in his speech, referencing the spirit of bipartisanship in Congress when the Senate passed the 1970 Clean Air Act with a unanimous vote.

“You can barely get that many votes to name a post office these days,” Obama joked. “This is a challenge that does not pause for partisan gridlock.”

Obama was the 14th president to speak from the steps of Old North, the second oldest building at Georgetown. George Washington spoke at the same location when his nephews attended the university in 1797, while Abraham Lincoln addressed Union soldiers in 1861 and Bill Clinton spoke to the diplomatic corps in 1993.